Method and apparatus for negotiating security during handover between different radio access technologies

ABSTRACT

Solution for security negotiation during handover of a user equipment (UE) between different radio access technologies are provided. In the solution, the UE receives NAS security information and AS security information which are selected by the target system and then performs security negotiation with the target system according to the received NAS security information and AS security information. As such, the UE may obtain the key parameter information of the NAS and AS selected by a LTE system and perform security negotiation with the LTE system when the UE hands over from a different system, such as a UTRAN, to the LTE system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/079,350, filed on Nov. 13, 2013, which is a continuation of U.S.patent application Ser. No. 12/617,175, filed on Nov. 12, 2009, now U.S.Pat. No. 8,611,949. The U.S. patent application Ser. No. 12/617,175 is acontinuation of International Patent Application No. PCT/CN2008/070962,filed on May 14, 2008, which claims priority to Chinese PatentApplication No. 200710099176.7, filed on May 15, 2007, all of which arehereby incorporated by reference in their entireties.

FIELD OF THE INVENTION

The present invention relates to mobile communication, and inparticular, to a method and apparatus for negotiating security duringhandover between different radio access technologies.

BACKGROUND

In a mobile communication system, a User Equipment (UE) generally needsto handover between base stations when moving from a local base stationto a target base station. The Radio Access Networks (RANs) of basestations include: Second Generation (2G) system, Third Generation (3G)system, and the Long Term Evolution (LTE) system to be launched in thefuture. The security protection levels and protection measures between aUE and a RAN are different from those between the UE and another RAN.

FIG. 1 shows structure of two security-related layers in the LTE system.As shown in FIG. 1, the Xu interface, S1-C interface, S1-U interface,and X2 interface have security requirement. In an LTE system, the basestation is in a locale vulnerable to attacks. Therefore, the basestation is not as secure as the Radio Network Controller (RNC) in theUniversal Mobile Telecommunications System (UMTS).

In the process of base station handover between the 2G system and the 3Gsystem, the UE needs to negotiate the security parameters as regardsonly the access layer with the base station in the 2G system or 3Gsystem. In the process of base station handover from the 2G or 3G systemto the LTE system, more security information needs to be negotiatedbetween the UE and the LTE system, and a higher security level is alsorequired. The UE needs to negotiate the security parameters as regardsboth the access layer and the non-access layer with the base station ofthe LTE system. Therefore, security is crucial for the base stationhandover from a 2G system or 3G system to an LTE system.

FIG. 2 is a flowchart of negotiating security between the UE and the 2Gsystem or 3G system in the process of base station handover between the2G system and the 3G system in the conventional art. The negotiationprocess includes the following steps:

Step 1: The source Base Station Subsystem (BSS) of the UE decides toinitiate a handover request according to the measurement report of theUE.

Step 2: The source BSS sends the UE capability information (includingthe integrity protection algorithm and encryption algorithm supported bythe UE) and the key information to the Serving GPRS Support Node (SGSN)of 2G system.

Step 3: The SGSN of 2G system sends the received UE capabilityinformation and the key information to the SGSN of 3G system.

Step 4: The SGSN of 3G system sends the received key information and thealgorithm supported by the UE to a RNC.

Step 5: According to the received key information and the algorithmsupported by the UE, the RNC selects the algorithm supported by the RNCand sends it to the SGSN of 3G system.

Step 6: The SGSN of 3G system sends the algorithm supported by the RNCto the SGSN of 2G system.

Afterward, at the time of sending a handover request acknowledgement tothe source access network of the UE, the SGSN of 2G system sends thealgorithm supported by the 3G SGSN to the source access network. At thetime of sending a handover command to the UE, the source access networksends the algorithm to be used by the target system to the UE, thuscompleting security negotiation.

In the process of implementing the present invention, the inventor findsthat the LTE system has two security-related strata: Non Access Stratum(NAS), and Access Stratum (AS). During handover between the 2G systemand the 3G system, the security information handled at the SGSN siderelates to the AS only, without relating to the NAS. Therefore, theforegoing process of negotiation between the UE and the 2G system or 3Gsystem cannot be applied to the UE handover from the 2G system or 3Gsystem to the LTE system. That is, no handover solution is currentlyavailable to ensure secure handover of the base station from the 2Gsystem or 3G system to the LTE system.

SUMMARY

The embodiments of the present invention are directed to providing amethod and apparatus for negotiating security during handover betweendifferent radio access technologies. When the UE hands over from adifferent system to an LTE system, the UE obtains the securityinformation of the NAS and AS selected by the LTE system, and performssecurity negotiation with the LTE system.

The objectives of the embodiments of the present invention are fulfilledthrough the following technical solution.

A method for negotiating security during handover between differentradio access technologies includes: transmitting the securityinformation of the NAS and security information of AS selected by thetarget system to the UE when the UE hands over between different radioaccess technologies, so that the UE can perform security negotiationwith the target system according to the security information of the NASand security information of AS.

An eNB device includes: (1) a key and algorithm information receivingunit, adapted to receive through a handover request the following sentby a target Mobile Management Entity (MME): parameters used in NAS keyderivation and algorithm information, parameters used in a eNB keyderivation, the eNB key and UE capability information; (2) an algorithmselecting and key deriving unit, adapted to select a supported RadioResources Control (RRC) encryption algorithm of the eNB, an integrityprotection algorithm of the eNB, and a User Plane (UP) encryptionalgorithm of the eNB according to information received by the key andalgorithm information receiving unit, and derive an RRC encryption keyand a UP encryption key; and (3) a transparent container incorporatingunit, adapted to include the following in a transparent container:parameters used in NAS key derivation and algorithm information obtainedby the key and algorithm information receiving unit, parameters used ineNB key derivation, and the RRC encryption key, the UP encryption key,the RRC encryption algorithm of the eNB, the integrity protectionalgorithm of the eNB, and the UP encryption algorithm of the eNB thatare obtained by the algorithm selecting and key deriving unit.

An eNB device includes: (1) a key and algorithm information receivingunit, adapted to receive through a handover request the following sentby a target MME: a NAS container, an eNB key (K_(eNB)), and UEcapability information; (2) an algorithm selecting and key derivingunit, adapted to select a RRC encryption algorithm of the eNB, anintegrity protection algorithm of the eNB, and a UP encryption algorithmof the eNB according to the K_(eNB) and the UE capability informationreceived by the key and algorithm information receiving unit, and derivean RRC encryption key and a UP encryption key; and (3) a transparentcontainer incorporating unit, adapted to include parameters used in theRRC encryption key derivation and UP encryption key derivation, the RRCencryption algorithm of the eNB, the integrity protection algorithm ofthe eNB, and the UP encryption algorithm of the eNB obtained by thealgorithm selecting and key deriving unit in an RRC container, andinclude the RRC container and the NAS container in a transparentcontainer.

A source access network device includes: (1) a NAS container receivingunit, adapted to receive an NAS container sent by a target MME; (2) aRRC container incorporating unit, adapted to receive an RRC containersent by the target MME; and (3) a transparent container incorporatingunit, adapted to include the NAS container received by the NAS containerreceiving unit and the RRC container received by the RRC containerincorporating unit in a transparent container.

A target MME includes: (1) an algorithm selecting and key deriving unit,adapted to derive a NAS key (K_(NAS)) and an eNB key (K_(eNB)) accordingto received key information used by a source system, and select a NASalgorithm; and send the K_(eNB) and UE capability information to atarget, eNB through a handover request; (2) an NAS containerincorporating unit, adapted to include the NAS algorithm, and parametersused in K_(NAS) derivation, and the parameters used in K_(eNB)derivation in an NAS container; and (3) a transparent containerincorporating unit, adapted to receive a RRC container sent by thetarget eNB; and include the RRC container and the NAS container in atransparent container.

A UE includes: (1) a unit adapted to receive a transparent container andobtain the NAS security information of and AS security information fromthe received transparent container; and (2) a unit adapted to performsecurity negotiation with the target system according to the contents inthe transparent container.

The technical solution provided in the embodiments of the presentinvention reveals that in the embodiments of the present invention, thesecurity information of the NAS and the security information AS istransmitted to the UE. Therefore, when the UE hands over to the LTEsystem, the UE obtains the security information of the NAS and thesecurity information AS selected by the LTE system, performs securitynegotiation with the LTE system, and creates a security associationbetween the UE and the LTE system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows structure of two security-related strata in the LTE systemin the conventional art;

FIG. 2 is a flowchart of negotiation between the UE and the 2G system or3G system in the process of base station handover between a 2G systemand a 3G system in the conventional art;

FIG. 3 is a flowchart of negotiation between a UE and an LTE system whenthe UE hands over from a UTRAN to an LTE system in the first embodimentof the present invention;

FIG. 4 is a flowchart of negotiation between a UE and an LTE system whenthe UE hands over from a UTRAN to an LTE system in the second embodimentof the present invention;

FIG. 5 shows structure of an eNB device provided in an embodiment of thepresent invention;

FIG. 6 shows structure of an access network device provided in anembodiment of the present invention; and

FIG. 7 shows structure of a target MME provided in an embodiment of thepresent invention.

DETAILED DESCRIPTION

A method and an apparatus for negotiating security during handoverbetween different radio access technologies are provided in anembodiment of the present invention.

The UE handover between different radio access technologies hereinincludes the UE handover from a different system to an LTE system. Themethod and apparatus provided in the embodiments of the presentinvention are described below, supposing that the UE hands over from aUTRAN system to an LTE system.

In the embodiments of the present invention, when the UE hands over fromthe UTRAN system to the LTE system, the target MME generates NASsecurity information and sends the NAS security information to thetarget eNB. The target eNB also generates AS security information, andcreates a transparent container according to the NAS securityinformation and the AS security information.

FIG. 3 is a flowchart of negotiating security between a UE and an LTEsystem when the UE hands over from a UTRAN to an LTE system in the firstembodiment of the present invention. The negotiating process includesthe following steps:

Step 31: First, the source system of the UE decides to perform ahandover procedure, and initializes a handover request.

Step 32: The source SGSN sends the handover request to the target MME.The handover request includes the UE capability information (including alist of NAS algorithm of the UE, RRC algorithm of the UE, and UPalgorithm of the UE) and the key information currently used by thesource system (or the key derived by the source system according to thecurrently used key information).

Step 33: According to the received key information, the target MMEderives an Access Security Management Entity (ASME) key K_(ASME), an NASkey K_(NAS), and an eNB key K_(eNB), and selects an NAS algorithm.

Step 34: The target MME sends the parameters used in K_(ASME)derivation, parameters used in K_(NAS) derivation, parameters used inK_(eNB) derivation, the K_(eNB), the selected NAS algorithm, and thelist of the RRC algorithm of the UE and UP algorithm of the UE to thetarget eNB through the handover request.

Step 35: The target eNB selects RRC encryption algorithm of the targeteNB, integrity protection algorithm of the target eNB, and UP encryptionalgorithm of the target eNB, and derives an RRC encryption key, anintegrity key, and a UP encryption key according to the receivedK_(eNB).

The target eNB shall create a transparent container including:parameters used in the RRC encryption key derivation and the UPencryption key derivation; the received parameters used in K_(ASME)derivation, parameters used in K_(NAS) derivation, parameters used inK_(eNB) derivation; the RRC algorithm of the UE and UP algorithm of theUE; the RRC encryption algorithm selected by the target eNB, integrityprotection algorithm selected by the target eNB, and UP encryptionalgorithm selected by the target eNB.

Step 36: The target eNB sends the transparent container to the targetMME.

Step 37: The target MME sends the transparent container to the sourceSGSN through a handover response.

Step 38: The source SGSN transmits the received transparent container tothe source access network through a handover response.

Step 39: The source access network transmits the contents of thereceived transparent container to the UE through a handover command

Step 310: According to the parameters used in the RRC encryption keyderivation and the UP encryption key derivation, the parameters used inK_(ASME) derivation, the parameters used in K_(NAS) derivation, theparameters used in K_(eNB) derivation in the received contents of thetransparent container, the UE derives the RRC encryption key, UPencryption key, K_(ASME), K_(NAS), and K_(eNB), and sets a protectionalgorithm applicable after handover.

FIG. 4 is a flowchart of negotiating security between a UE and an LTEsystem when the UE hands over from a UTRAN to an LTE system in thesecond embodiment of the present invention. The negotiating processincludes the following steps:

Step 41: First, the source system of the UE decides to perform ahandover procedure, and initializes a handover request.

Step 42: The source SGSN sends the handover request to the target MME.The handover request includes the UE capability information (including alist of the NAS algorithm of the UE, RRC algorithm of the UE, and UPalgorithm of the UE), and the key information currently used by thesource system (or a processed key).

Step 43: According to the received key information, the target MMEderives a K_(ASME), a K_(NAS), and a K_(eNB), and selects an NASalgorithm. The target MME includes the selected NAS algorithm,parameters used in K_(ASME) derivation, parameters used in K_(NAS)derivation, and parameters used in K_(eNB) derivation in an NAScontainer.

Step 44: The target MME sends the K_(eNB), the list of RRC algorithm ofthe UE and UP algorithm of the UE, and the NAS container to the targeteNB through the handover request.

Step 45: The target eNB selects the RRC encryption algorithm of thetarget eNB, integrity protection algorithm of the target eNB, and UPencryption algorithm of the target eNB, and derives an RRC encryptionkey, an integrity key, and a UP encryption key according to the receivedK_(eNB).

The target eNB includes the following into an RRC container: parametersused in the RRC encryption key derivation and UP encryption keyderivation; the RRC algorithm of the UE and UP algorithm of the UE; theRRC encryption algorithm selected by the target eNB, integrityprotection algorithm selected by the target eNB, and the UP encryptionalgorithm selected by the target eNB. The RRC container and the receivedNAS container are included in a transparent container.

Step 46: The target eNB sends the transparent container to the targetMME.

Step 47: The target MME sends the transparent container to the sourceSGSN through a handover response.

Step 48: The source SGSN transmits the received transparent container tothe source access network through a handover command.

Step 49: The source access network transmits the contents of thereceived transparent container to the UE transparently through ahandover command

Step 410: According to the parameters used in the RRC encryption keyderivation and UP encryption key derivation, the parameters used inK_(ASME) derivation, the parameters used in K_(NAS) derivation, and theparameters used in K_(eNB) derivation in the received contents of thetransparent container, the UE derives the corresponding RRC encryptionkey, UP encryption key, K_(ASME), K_(NAS), and K_(eNB), and sets therelevant algorithm applicable after handover.

The process of negotiating security between a UE and an LTE system whenthe UE hands over from a UTRAN to an LTE system in the third embodimentof the present invention includes the following steps:

Step 51: First, the source system of the UE decides to perform ahandover procedure, and initializes a handover request. Afterward, thesource SGSN sends the handover request to the target MME. The handoverrequest includes the UE capability information (including a list of theNAS algorithm of the UE, RRC algorithm of the UE, and UP algorithm ofthe UE), and the key information currently used by the source system (ora processed key).

Step 52: According to the received key information, the target MMEderives a K_(ASME), a K_(NAS), and a K_(eNB), and selects an NASalgorithm. The target MME includes the selected NAS algorithm,parameters used in K_(ASME) derivation, parameters used in K_(NAS)derivation, and parameters used in K_(eNB) derivation in an NAScontainer. Afterward, the target MME sends the K_(eNB), the list of RRCalgorithm of the UE and UP algorithm of the UE, and the NAS container tothe target eNB through the handover request.

Step 53: The target eNB selects RRC encryption algorithm of the targeteNB, integrity protection algorithm of the target eNB, and UP encryptionalgorithm of the target eNB, and derives an RRC encryption key, anintegrity key, and a UP encryption key according to the receivedK_(eNB).

Afterward, the target eNB includes the following contents in atransparent container: parameters used in the RRC encryption keyderivation and UP encryption key derivation; the RRC algorithm of the UEand UP algorithm of the UE; the RRC encryption algorithm selected by thetarget eNB, integrity protection algorithm selected by the target eNB,the UP encryption algorithm selected by the target eNB, and the receivedNAS container. Then, the target eNB sends the transparent container tothe target MME.

Step 54: The target MME sends the transparent container to the sourceSGSN through a handover response. The source SGSN transmits the receivedtransparent container to the source access network through a handovercommand The source access network transmits the contents of the receivedtransparent container to the UE through a handover command.

Step 55: According to the parameters used in the RRC encryption keyderivation and UP encryption key derivation, the parameters used inK_(ASME) derivation, the parameters used in K_(NAS) derivation, andparameters used in K_(eNB) derivation in the received contents of thetransparent container, the UE derives the RRC encryption key, UPencryption key, K_(ASME), K_(NAS), and K_(eNB), and sets the relevantalgorithm applicable after handover.

The process of negotiating security between a UE and an LTE system whenthe UE hands over from a UTRAN to an LTE system in the fourth embodimentof the present invention includes the following steps:

Step 61: First, the source system of the UE decides to perform ahandover procedure, and initializes a handover request. Afterward, thesource SGSN sends the handover request to the target MME. The handoverrequest includes the UE capability information (including a list of theRRC algorithm of the UE, and UP algorithm of the UE) and the keyinformation currently used by the source system (or a processed key).

Step 62: According to the received key information, the target MMEderives a K_(ASME), a K_(NAS), and a K_(eNB), and selects an NASalgorithm.

Afterward, the target MME sends the list of the RRC algorithm of the UEand UP algorithm of the UE as well as the K_(eNB) to the target eNB. Thetarget MME includes the selected NAS algorithm, parameters used inK_(ASME) derivation, parameters used in K_(NAS) derivation, andparameters used in K_(eNB) derivation in an NAS container, and sends theNAS container to the source access network through the source SGSN.

Step 63: The target eNB selects RRC encryption algorithm of the targeteNB, integrity protection algorithm of the target eNB, and UP encryptionalgorithm of the target eNB; and derives an RRC encryption key, anintegrity key, and a UP encryption key according to the receivedK_(eNB).

The target eNB includes the following in an RRC container: parametersused in the RRC encryption key derivation and UP encryption keyderivation; the RRC algorithm of the UE and UP algorithm of the UE; theRRC encryption algorithm selected by the target eNB and integrityprotection algorithm selected by the target eNB, and the UP encryptionalgorithm selected by the target eNB. Then, the target eNB sends thecontents of the RRC container to the target MME.

Step 64: The target MME sends the contents of the RRC container to thesource SGSN through a handover response, and the source SGSN transmitsthe received RRC container to the source access network through ahandover command.

The source access network sends the contents of the received NAScontainer and the contents of the RRC container to the UE.

Step 65: According to the parameters used in the RRC encryption keyderivation and UP encryption key derivation, the parameters used inK_(ASME) derivation, the parameters used in K_(NAS) derivation, and theparameters used in K_(eNB) derivation in the contents of the receivedNAS container and RRC container, the UE derives the corresponding RRCencryption key, UP encryption key, K_(ASME), K_(NAS), and K_(eNB), andsets the relevant algorithm applicable after handover.

The process of negotiating security between a UE and an LTE system whenthe UE hands over from a UTRAN to an LTE system in the fifth embodimentof the present invention includes the following steps:

Step 71: First, the source system of the UE decides to perform ahandover procedure, and initializes a handover request. Afterward, thesource SGSN sends a handover request to the target MME. The handoverrequest includes the UE capability information (including a list of theRRC algorithm of the UE, and UP algorithm of the UE), and the keyinformation currently used by the source system (or a processed key).

Step 72: According to the received key information, the target MMEderives a K_(ASME), a K_(NAS), and a K_(eNB), and selects an NASalgorithm.

The target MME sends the UE capability information and K_(eNB) to thetarget eNB, and includes parameters used in K_(ASME) derivation,parameters used in K_(NAS) derivation, and parameters used in K_(eNB)derivation as well as the NAS algorithm in an NAS container.

Step 73: The target eNB selects RRC encryption algorithm of the targeteNB, integrity protection algorithm of the target eNB, and UP encryptionalgorithm of the target eNB; and derives an RRC encryption key, anintegrity key, and a UP encryption key according to the receivedK_(eNB).

The target eNB includes parameters used in the RRC encryption keyderivation and UP encryption key derivation, the RRC encryptionalgorithm of the target eNB, integrity protection algorithm of thetarget eNB and UP encryption algorithm of the target eNB in an RRCcontainer, and sends the RRC container to the target MME. The target MMEincludes the RRC container and the NAS container in a transparentcontainer, and sends the transparent container to the source accessnetwork through a source SGSN.

The source access network sends the contents of the received transparentcontainer to the UE.

Step 74: According to the parameters used in the RRC encryption keyderivation and UP encryption key derivation, the parameters used inK_(ASME) derivation, the parameters used in K_(NAS) derivation, and theparameters used in K_(eNB) derivation in the contents of the receivedNAS container and RRC container, the UE derives the corresponding RRCencryption key, UP encryption key, K_(ASME), K_(NAS), and K_(eNB), andsets the relevant algorithm applicable after handover.

The processes of the embodiment 1, embodiment 2, embodiment 3 andembodiment 4 suppose that the UE hands over from the UTRAN to the LTEsystem, and are also applicable to the scenario of handover from a 2Gnetwork to an LTE network, where both the 2G network and the 3G networkare called a Packet Switched (PS) domain.

If the UE hands over from a Circuit Switched (CS) domain of the 2G/3G toan LTE system, the process of security negotiation between the UE andthe LTE network needs to be decided according to the specific handoverprocess of the UE.

When the UE hands over from the CS domain of the 2G/3G system to the LTEsystem, if the UE is disconnected from the CS domain of the 2G/3G systemand then connected with the LTE system again, the UE may perform anAuthentication and Key Agreement (AKA) process with the LTE systemdirectly, and then obtain the corresponding NAS security information andAS security information from the LTE system.

When the UE hands over from the CS domain of the 2G/3G system to the LTEsystem, if the UE hands over from the CS domain of the 2G/3G system tothe PS domain of the 2G/3G system and then hands over to the LTE systemsmoothly, the process of security association negotiated between the UEand LTE system is the same as that in the foregoing process of handoverfrom the PS domain of the 2G/3G system to the LTE system.

When the UE hands over from the CS domain of the 2G/3G system to the LTEsystem, if the UE hands over from the CS domain of the 2G/3G system tothe LTE system, the security association negotiated between the UE andthe LTE system is transferred through a Mobile Services Switching Center(MSC) node and a target MME, thus facilitating the UE to obtain thecorresponding NAS security information and AS security information.

When the UE hands over from the CS domain of the 2G/3G system to the LTEsystem, if the UE hands over from the IP Multimedia Subsystem (IMS) onthe CS domain of the 2G/3G system to the LTE system first, the securityassociation negotiated between the UE and the LTE system is transferredthrough a Call Session Control Function (CSCF) node of the IMS and atarget MME, thus facilitating the UE to obtain the corresponding NASsecurity information and AS security information.

As shown in FIG. 5, an eNB device provided in an embodiment of thepresent invention includes: (1) a key and algorithm informationreceiving unit, adapted to receive through a handover request thefollowing sent by a target Mobile Management Entity (MME): parametersused in Non Access Stratum (NAS) key derivation and algorithminformation, parameters used in a eNB key derivation, the eNB key andUser Equipment (UE) capability information; (2) an algorithm selectingand key deriving unit, adapted to select RRC encryption algorithm of theeNB, integrity protection algorithm of the eNB, and UP encryptionalgorithm of the eNB according to the information received by the keyand algorithm information receiving unit, and derive an RRC encryptionkey and a UP encryption key; and (3) a transparent containerincorporating unit, adapted to includes the following in a transparentcontainer: the parameter and algorithm information of the NAS key andthe parameter and algorithm information of the AS key obtained by thekey and algorithm information receiving unit; and the RRC encryptionkey, UP encryption key, RRC encryption algorithm of the eNB, integrityprotection algorithm of the eNB, and UP encryption algorithm of the eNBthat are obtained by the algorithm selecting and key deriving unit.

An eNB device is provided in an embodiment of the present invention. Asshown in FIG. 5, the eNB device includes: (1) a key and algorithminformation receiving unit, adapted to receive through a handoverrequest the following sent by a target Mobile Management Entity (MME): aNon Access Stratum (NAS) container, an eNB key (K_(eNB)), and UserEquipment (UE) capability information sent; (2) an algorithm selectingand key deriving unit, adapted to select RRC encryption algorithm of theeNB, integrity protection algorithm of the eNB, and UP encryptionalgorithm of the eNB according to the K_(eNB) and UE capabilityinformation received by the key and algorithm information receivingunit, and derive an RRC encryption key and a UP encryption key; and (3)a transparent container incorporating unit, adapted to includeparameters used in the RRC encryption key derivation and UP encryptionkey derivation, RRC encryption algorithm of the eNB, integrityprotection algorithm of the eNB, and UP encryption algorithm of the eNBobtained by the algorithm selecting and key deriving unit in an RRCcontainer; and include the RRC container and the NAS container in atransparent container.

A source access network device is provided in an embodiment of thepresent invention. As shown in FIG. 6, the source access network deviceincludes: (1) an NAS container receiving unit, adapted to receive an NAScontainer sent by the target MME; (2) an RRC container incorporatingunit, adapted to receive an RRC container sent by the target MME; and(3) a transparent container incorporating unit, adapted to include theNAS container received by the NAS container receiving unit and the RRCcontainer received by the RRC container incorporating unit in atransparent container.

A target MME is provided in an embodiment of the present invention. Asshown in FIG. 7, the target MME includes: (1) an algorithm selecting andkey deriving unit, adapted to derive a K_(NAS) and a K_(eNB) accordingto the received key information used by the source system, and select anNAS algorithm; and send the K_(eNB) and UE capability information to thetarget eNB through a handover request; (2) an NAS containerincorporating unit, adapted to include the NAS algorithm, and theparameters used in K_(NAS) derivation, and the parameters used inK_(eNB) derivation in an NAS container; and (3) a transparent containerincorporating unit, adapted to receive the RRC container sent by thetarget eNB, and include the RRC container and the NAS container in atransparent container.

To sum up, in the embodiments of the present invention, the securityinformation of the NAS and AS is transmitted to the UE. Therefore, whenthe UE hands over from a 3G or 2G system, such as Universal TerrestrialRadio Access Network (UTRAN), to the LTE system, the UE obtains thesecurity information of the NAS and AS selected by the LTE system,performs security negotiation with the LTE system, and creates asecurity correlation between the UE and the LTE system.

Furthermore, a transparent container may be generated out of thesecurity information of the NAS and AS selected by the LTE system, thecapability information supported by the UE, and the encryption algorithmselected by the target eNB, and the transparent container is transmittedto the UE. Therefore, when the UE hands over from the UTRAN to the LTEsystem, the UE obtains the parameter information of the NAS key and ASkey selected by the LTE system, and the encryption algorithm selected bythe target eNB. The UE negotiates the NAS and AS security parameters andthe security algorithm between the LTE system and a different systemwithout adding any signaling, and a security correlation is createdbetween the UE and the LTE system.

The embodiments of the present invention are compatible with thehandover signaling flow between the 2G system and the 3G system, andimplement negotiation of the NAS and AS security parameters and thesecurity algorithm between the LTE system and a different system withoutadding any extra signaling.

It is understandable to those skilled in the art that the processes inthe foregoing embodiments may be implemented by hardware instructed by aprogram. The program may be stored in a readable storage medium. Oncebeing executed, the program performs the steps covered by the foregoingmethods. The storage medium may be a ROM/RAM, magnetic disk or compactdisk.

Although the invention has been described through some exemplaryembodiments, the invention is not limited to such embodiments. It isapparent that those skilled in the art can make various modificationsand variations to the invention without departing from the spirit andscope of the invention. The invention is intended to cover themodifications and variations provided that they fall in the scope ofprotection defined by the following claims or their equivalents.

What is claimed is:
 1. A method applied during a handover of a userequipment (UE) from a source system to a target system, the methodcomprising: selecting, by a mobility management network element in thetarget system, a non access stratum (NAS) algorithm; sending, by themobility management network element, the NAS algorithm to a base stationin the target system; selecting, by the base station, an access stratum(AS) algorithm; including, by the base station, the NAS algorithm andthe AS algorithm in a transparent container; sending, by the basestation, the transparent container to the mobility management networkelement; and sending, by the mobility management network element, thetransparent container to the UE through the source system; wherein radioaccess technologies supported by the source system and the target systemare different.
 2. The method according to claim 1, further comprising:receiving, by the mobility management network element, key informationused by the source system; deriving, by the mobility management networkelement, an access security management entity key (K_(ASME)), an NAS key(K_(NAS)) and an evolved Node B (eNB) key (K_(eNB)) according to the keyinformation used by the source system; and sending, by the mobilitymanagement network element, the K_(eNB), and a parameter used in thederivation to the base station; including, by the base station, theparameter used in the derivation in the transparent container.
 3. Themethod according to claim 2, further comprising: receiving, by themobility management network element, UE capability information from thesource system; sending, by the mobility management network element, theUE capability information to the base station.
 4. The method accordingto claim 1, wherein the source system is a second generation (2G) systemor a third generation (3G) system, the target system is a long termevolution (LTE) system, the mobility management network element is amobility management entity (MME), and the base station is an eNB.
 5. Themethod according to claim 1, wherein sending the NAS algorithm to thebase station in the target system comprises: sending, by the mobilitymanagement network element, the NAS algorithm to the base station in thetarget system through a handover request message.
 6. The methodaccording to claim 5, wherein sending the transparent container to themobility management network element comprises: sending, by the basestation, the transparent container to the mobility management networkelement through a handover response message.
 7. The method according toclaim 1, wherein sending the transparent container to the UE through thesource system comprises: sending, by the mobility management networkelement, the transparent container to a serving GPRS support node (SGSN)in the source system; sending, by the SGSN, the transparent container toan access network in the source system, to enable the access network tosend the transparent container to the UE.
 8. The method according toclaim 1, wherein the AS algorithm comprises a radio resources control(RRC) algorithm and a user plane (UP) algorithm.
 9. The method accordingto claim 8, further comprising: deriving, by the base station, a key forthe RRC algorithm and a key for the UP algorithm.
 10. The methodaccording to claim 8, wherein the RRC algorithm comprises an RRCencryption algorithm and an RRC integrity algorithm, the UP algorithmcomprises an UP encryption algorithm.
 11. A communication systemcomprising a mobility management network element and a base station,wherein, during a handover of a user equipment (UE) from a source systemto the communication system, the mobility management network element isconfigured to select a non access stratum (NAS) algorithm, and send theNAS algorithm to the base station; the base station is configured toreceive the NAS algorithm, select an access stratum (AS) algorithm,include the NAS algorithm and the AS algorithm in a transparentcontainer, and send the transparent container to the mobility managementnetwork element; and the mobility management network element is furtherconfigured to send the transparent container to the UE through thesource system; wherein radio access technologies supported by the sourcesystem and the communication system are different.
 12. The communicationsystem according to claim 11, wherein, the mobility management networkelement is further configured to receive key information used by thesource system, derive an access security management entity key(K_(ASME)), an NAS key (K_(NAS)) and an evolved Node B (eNB) key(K_(eNB)) according to the key information used by the source system,and send the K_(eNB), and a parameter used in the derivation to the basestation; the base station is further configured to include the parameterused in the derivation in the transparent container.
 13. Thecommunication system according to claim 12, wherein the mobilitymanagement network element is further configured to receive UEcapability information from the source system, and send the UEcapability information to the base station.
 14. The communication systemaccording to claim 11, wherein the source system is a second generation(2G) system or a third generation (3G) system, the communication systemis a long term evolution (LTE) system, the mobility management networkelement is a mobility management entity (MME), and the base station isan eNB.
 15. The communication system according to claim 11, wherein themobility management network element is configured to send the NASalgorithm to the base station in the target system through a handoverrequest message.
 16. The communication system according to claim 15,wherein the base station is configured to send the transparent containerto the mobility management network element through a handover responsemessage.
 17. The communication system according to claim 11, wherein themobility management network element is configured to send thetransparent container to a serving GPRS support node (SGSN) in thesource system, the transparent container is sent by the SGSN to the UEthrough an access network in the source system.
 18. The communicationsystem according to claim 11, wherein the AS algorithm comprises a radioresources control (RRC) algorithm and a user plane (UP) algorithm. 19.The communication system according to claim 18, wherein the base stationis further configured to derive a key for the RRC algorithm and a keyfor the UP algorithm.
 20. The communication system according to claim19, wherein the RRC algorithm comprises an RRC encryption algorithm andan RRC integrity algorithm, the UP algorithm comprises an UP encryptionalgorithm.